Previous studies from our laboratory have demonstrated improved myocardial function and decreased heart work by the administration of a potent phosphodiesterase inhibitor, glucagon, and Sodium Nitroprusside following experimental coronary artery ligation and myocardial infarction. It is the objective of this research to continue observations on the hemodynamic effects of phosphodiesterase inhibition and infusion of the experimental inotropic drug, Dobutamine (E. Lilly Co.) following experimental coronary artery ligation. Since myocardial calcium concentration is implicated in cardiac contraction, the hemodynamic effects of calcium concentration changes will be studied before and following phosphodiesterase inhibition. Observations will be made following constant calcium ion infusion, as well as following calcium ion deficit by the administration of an appropriate chelating agent.